1. Field of the Invention
The present invention relates to a high-frequency wiring board for connecting and mounting a high-frequency integrated circuit or a high-frequency circuit device such as an IC and an LSI used in a high-frequency region of a millimeter waveband of 30 GHz or more, and more specifically, relates to a high-frequency wiring board which has a through conductor for signal transmission with an improved high-frequency signal transmission characteristic.
2. Description of the Related Art
As a conventional high-frequency wiring board which transmits a high-frequency signal, there is one which is shown in a section view of FIG. 7 and a plan view of FIG. 8, for example.
In FIGS. 7 and 8, reference numeral 21 denotes a high-frequency wiring board, reference numerals 22a to 22d denote dielectric layers, a first line conductor 23 and a second line conductor 24 are disposed to main faces 29a, 29b of the high-frequency wiring board 21, and one ends of the first and second line conductors 23, 24 are electrically connected to each other by a through conductor 25. Moreover, ground conductors 26 and same plane ground conductors 28 are disposed to main faces of the dielectric layers 22a to 22d, and the ground conductors 26 and the same plane ground conductors 28 are electrically connected by a plurality of ground through conductors 27.
More specifically, the high-frequency wiring board 21 comprises a dielectric board 22, the first line conductor 23, the second line conductor 24, the through conductor 25, the ground conductors 26, the ground through conductors 27 and the same plane ground conductors 28. The dielectric board 22 is formed by laminating the dielectric layers 22a, 22b, 22c, 22d. The first line conductor 23 is disposed onto the main face 29a of the dielectric layer 22a, which is a top face of the high-frequency wiring board 21, and the second line conductor 24 is disposed onto the main face 29b of the dielectric layer 22d, which is a bottom face of the high-frequency wiring board 21. One end 23a of the first line conductor 23 and one end 24a of the second line conductor 24 overlap each other when viewed from a thickness direction of the dielectric layers 22a to 22d, and the one ends 23a, 24a are electrically connected to each other by the through conductor 25 piercing the dielectric layers 22a to 22d. On the respective main faces defining interlayer border planes of the dielectric layers 22a to 22d, ground conductors 26 formed so as to surround the through conductor 25 are disposed with specified spaces to the through conductor 25. The same plane ground conductors 28 which are formed with a specified space from the first line conductor 23 on the main face 29a of the dielectric layer 22a with the first line conductor 23 formed and formed with a specified space from the second line conductor 24 on the main face 29b of the dielectric layer 22d with the second line conductor 24 formed are disposed. The ground conductors 26 and the same plane ground conductors 28 are electrically connected by the ground through conductors 27.
This high-frequency wiring board has a problem that because a frequency of a high-frequency signal becomes higher in recent years, unnecessary radiation of a high-frequency signal occurs from between the ground through conductors 27, with the result that radiation loss of a high-frequency signal increases and a transmission characteristic deteriorates.
Hence, as a technique of inhibiting unnecessary radiation of a high-frequency signal from between the ground through conductors 27, such a technique that, by setting the number of the ground through conductors 27 formed so as to surround the through conductor 25 to five or more, enables decrease of radiation loss of a high-frequency signal and improvement of a high-frequency signal transmission characteristic is proposed, for example (refer to Japanese Unexamined Patent Publication JP-A 5-206678 (1993)).
However, the above conventional high-frequency wiring board has a problem that although unnecessary radiation of a high-frequency signal from between the ground through conductors is inhibited as a result of increasing the number of the ground through conductors, a wavelength is short in a high-frequency region of a millimeter waveband, and therefore, a mode (a high-order mode) different from a basic propagation mode occurs at a point of the through conductor in a case where the length of the through conductor is xcex/4 or more, with the result that a transmission characteristic deteriorates greatly as a frequency becomes higher.
The invention was made in view of the above problems, and an object of the invention is to provide a high-frequency wiring board which is capable of inhibiting a high-order mode occurring at a point of a through conductor and enables obtaining a good transmission characteristic in a high-frequency signal of a millimeter waveband of 30 GHz or more.
The invention provides a high-frequency wiring board comprising:
a dielectric board formed by laminating a plurality of dielectric layers;
a first line conductor formed on a main face of one dielectric layer of the dielectric board;
a second line conductor formed on a main face of another dielectric layer of the dielectric board;
a through conductor for electrically connecting one end of the first line conductor to one end of the second line conductor by piercing the dielectric layers between the first line conductor and the second line conductor;
same plane ground conductors which are formed with a specified space from the first line conductor on the main face of the dielectric layer on which main face the first line conductor is formed and are formed with a specified space from the second line conductor on the main face of the dielectric layer on which main face the second line conductor is formed;
ground conductors formed on the main faces of the dielectric layers between the first line conductor and the second line conductor so as to surround the through conductor; and
a plurality of ground through conductors which are formed on the dielectric layers so as to surround the through conductor and which electrically connect the same plane ground conductors and the ground conductors,
wherein L greater than xcex/4 and xcfx80(A+B)xe2x89xa6xcex are satisfied in which
L is a length of the through conductor, A is a diameter of the through conductor, B is shortest distances between the through conductor and the ground through conductors, xcfx80 is a circle ratio and xcex is an effective wavelength of a high-frequency signal transmitted by the through conductor.
According to the invention, as described above, a diameter A and length L of the through conductor and shortest distances B between the through conductor and the ground through conductors are set within specified ranges with respect to an effective wavelength xcex of a high-frequency signal, so that even in the case of a long through conductor with a length of xcex/4 or more, distances between the through conductor and the ground through conductors are short enough with respect to an effective wavelength of a high-frequency signal, a standing wave and the like between the through conductor and the ground through conductors is hard to occur, it is possible to inhibit occurrence of a high-order mode at a point of the through conductor also in a high-frequency region of a millimeter waveband, and consequently, it is possible to realize a good transmission characteristic in a high-frequency signal of a millimeter waveband.
Further, in the invention it is preferable that in the above construction, a distance H between the ground conductor and the same plane ground conductor is equal to or less than xcex/2.
According to the invention, as a result that distances between the ground conductors and the same plane ground conductors, that is, connection lengths of the ground through conductors electrically connecting the ground conductors and the same plane ground conductors are made to be short enough with respect to a wavelength of a high-frequency signal, it is possible to inhibit potential distribution which occurs in the respective ground through conductors, so that it is possible to stabilize ground potential of the ground through conductors, and consequently, it is possible to realize a good transmission characteristic in a high-frequency signal of a millimeter waveband.
Still further, in the invention it is preferable that in the above respective constructions, a distance P between centers of the ground through conductors is equal to or less than xcex/4.
According to the invention, a distance between the centers of the ground through conductors is short enough with respect to an effective wavelength of a high-frequency signal, it is possible to inhibit spread of an electromagnetic field from between the ground through conductors, and therefore, it is possible to further inhibit unnecessary radiation of a high-frequency signal from between the ground through conductors, with the result that it is possible to realize a good transmission characteristic in a high-frequency signal of a millimeter waveband.
In the invention it is preferable that a frequency of the high-frequency signal is within a range from 30 GHz to 100 GHz.
As described above, according to the invention, it is possible to provide a high-frequency wiring board which is capable of inhibiting a high-order mode occurring at a point of the through conductor and enables obtaining a good transmission characteristic in a high-frequency signal of a millimeter waveband of 30 GHz or more.